The concept of a self-sharpening knife comes originally from observations of the incisors of rats. These teeth consist of a very hard, but very thin, front layer which is mechanically supported by a much thicker, but softer, tooth body. The sharpness of the cutting edge comes from the thinness of the hard front layer. The softer material wears away faster such that a steady state profile is maintained in normal use (gnawing) in which the tooth body slopes down away from the thin hard front cutting edge. It can never get dull because the hard layer has the same thickness down the whole length of the tooth, and it is this thickness that defines the cutting edge.
In conventional microknives made from a block of a single material (for example a diamond), the sharpness comes from the initial sharpening of the blade when it is manufactured. Even with diamond, the hardest material that exists, it is just a matter of time before atoms are worn away from the cutting edge and it becomes dull. Although diamond knives can be re-sharpened, it is difficult, requiring special skill and tools.
A self-sharpening layered knife construction (for use in large supporting structure such as the conventional sized saws and razors) is discussed in U.S. Pat. Nos. 6,105,261 and 6,389,699, the entirety of each of which is incorporated by reference. To be self-sharpening, the sharpness must come from the geometry of the construction, not the initial edge grinding. The required geometry is a thin layer of a hard material supported by a thicker layer (or layers) of softer material. The relative thinness of the hard layer is directly related to the degree of sharpness of such knives. However, the references referred to above, teach of traditional fabrication techniques and do not teach knives having a sharpness measured at the atomic level.
In fact, the use of metals to fabricate a micro-knife of atomic level dimensions is not possible because metals undergo plastic deformation at the stresses that will be encountered in cutting tissue or other materials at the atomic level. For example, a micro-knife having, dimensions 1 mm long, 0.020 mm thick, and 0.5 mm wide (and fabricated through powder metallurgy, electroplating, or diffusion bonding, etc.) is simply unsuitable for atomic level procedures. Such a knife will just be a thin piece of foil that irreversibly bends and deforms given the typical stresses encountered in such procedures.
With powder metallurgy, the starting material is a granular powder for which the size of the individual particles is greater than 1 micron. After the granular powder is compressed and heated to make a solid part, the minimum achievable layer is about 1,000 angstroms. Moreover, it is unlikely that, at the atomic level, the surface will be smooth, well defined, and of a constant thickness since it was made from relatively “lumpy” particles.
Fabrication of a blade that has a meaningful thin layer less than 500 angstroms thick requires a supporting substrate having as surface roughness less than, for example, 500 angstroms. This is not practical with a metallic substrate. Instead, substrates manufactured from ceramics, glass, and silicon are more practical to achieve angstrom-scale smooth substrates suitable for producing thin films a few angstroms thick.
In addition, the large coefficient of thermal expansion of metals greatly limits the temperature at which thin layers can be deposited without cracking upon cooling.
In view of the above, conventional metal, diamond tipped or other similar type knives have blade edges or cutting surfaces that are considerably large when viewed on an atomic scale. Typically such knives have cutting edges ranging from 500 angstroms to about 1000 angstroms. Typically, such knives provide poor surgical precision and cause unnecessary destruction of tissue when viewed at the cellular level.
Presently, atomic force microscopy uses devices having atomically sharp-tips for the manipulation and separation of cells. Such devices and methods are found in U.S. Pat. Nos. 5,221,415; 5,399,232; and 5,994,160 the entirety of each of which are incorporated by reference herein. Additional information regarding devices used in atomic force microscopy may be found in Journal of Nanoscience and Nanotechnology 2002, V 2, No. 1, pp 55-59, and Journal of Microelectromechanical Systems V 6, No. 4, December 1997, pp: 303-306 the entirety of which are also both incorporated by reference herein.
References describing the fabrication of micro knives from single crystal silicon include U.S. Pat. Nos. 5,728,089; 5,317,938; 5,579,583; 5,792,137; 5,842,387; 5,928,161; 5,944,717; 5,980,518; 6,319,474; 6,615,496; 6,706,203; and U.S. patent application nos.: 20020078576; 20030208911; 20050132581; and 20050144789 the entirety of each of which is incorporated by reference herein. Most conventional micro-knives rely on silicon as the cuttinz blade. Problems may be encountered as silicon wears too rapidly to provide a satisfactory cutting surface. As a result, silicon tends to dull quickly. Commonly assigned U.S. Provisional application No. 60/741,200 entitled: MICRO SURGICAL CUTTING INSTRUMENTS, filed on Dec. 1, 2005, the entirety of which is incorporated by reference herein, teaches improved atomic level knives and blades.
Accordingly, there remains a need for an improved atomic level microsurgical Cutting instrument that is designed to provide self-sharpening features.